Bug: What was a working scene stops working after closing and restarting Unity

DSC

I get the following console alert

"NullReferenceException:Object reference not set to an instance of an object

PlayerMovement.LateUpdate () (at Assets/AdventureCreator/Scripts/Controls/PlayerMovement.cs:103)"

I have encountered this several times today. After getting everything in the scene to work I save it and close Unity. When I reopen Unity and this scene I get this error. I rebuilt the scene the first time. I removed the player prefab and reimported the robot player from the demo and set up all of the player camera and movement constraints again the second time. This third time I decided to contact you. I'm hopeful you can help.

Thanks,

David